Insulin-dependent (Type I) diabetes mellitus develop after nearly all beta cells in the pancreatic islets have disappeared. The other hormone producing islet cells are apparently left unaffected. The onset of the disease is associated with islet auto-immunity since many patients have insulitis, hypersensitivity against islet cell antigens and islet autoantibodies detected in an array of different assays including those of insulin autoantibodies. It is unclear whether cellular or humoral autoimmunity are of pathogenetic importance but autoantibodies against islet cells have been detected in selected individuals several years before the clinical onset. Insulin-dependent diabetes would therefore, represent a chronic autoimmune disorder which develop in individuals who have certain HLA-DQ specificities and might be triggered by environmental factors such as mumps, rubella or certain chemicals. The long term objective is to determine which molecule(s) represent the target for the beta-cell specific autoimmune reaction. Such molecules need to be identified and isolated to be used in effective screening assays for islet cell specific autoantibodies and to develop measures which inhibit the islet cell autoreactivity. Susceptible individuals need to be identified by effective screening methods for both islet cell antibodies as proposed in this project and HLA-DQ susceptibility genes, since only 10% of newly diagnosed insulin dependent diabetic children have a first degree relative with the disease. The specific aims include attempts to obtain amino acid sequence information of an islet Mr 64,000 protein, found to be both immunoprecipitated and detected by immunoblotting with diabetes sera. The possible beta cell specificity of this protein will be determined by similar analyses of other tissues. The possible presence of a Mr 64,000 component in soluble immune complexes from newly diagnosed patients will be analyzed. Attempts will be made to raise monoclonal antibodies against the Mr 64,000 protein also to be used in immunoscreening of expression libraries to identify and characterize the gene. Methods designed to screen for Mr 64,000 autoantibodies will be developed and tested on well- defined sera collected from incident cases and referents of diabetic children, in order to define the predictive value of the antibody test. The spontaneously diabetic BB rat will be used to develop methods to test whether antigen-specific immunesuppression will prevent a later onset of diabetes.